The shuttle is great - potters around the bay and stops at about ten bars/restaurants. Takes about an hour to do the complete circuit and the is nothing nicer than sitting in the sun on the shuttle with your glass of wine to hand.
You can get on and off as many times as you like, day ticket is $5 and wine some silly price. It really is excellent and the guys running it deserve to do well
If you are not staying at one of the bay front hotels it is still an easy walk from areas like 5th Avenue
A "Must do" for Naples - and, my wife is still talking to me